Thermostatic switch



Feb. 26, 1952 R, M, MANNlNG 2,587,351

THERMOSTATIC SWITCH Filed ot. 24, 195o l5 Mad/570x I l l 5; 37 lla ITWVSTTOTY ,9 Ralph M. Manning.

/ H is Abbarney.

Patented Feb. 26, 195,2

THERMOSTATIC SWITCH Ralph M. Manning, West Medford, Mass., assignor to General Electric Company, a corporation of New York Application october 24, 195o, serial No. 191,858

3 Claims.

This invention relates to condition responsive switches, and particularly to room thermostats such as are used for energizing the electrical control circuits in domestic heating and air conditioning installations, although certain of the improvements of the present invention may be useful in other types of condition responsive contro1 devices.

The object of my invention is to provide an improved thermostat which is simple and rugged in construction, r-eliable in operation, inexpensive to manufacture, and easy to install and maintain, and which provides simple calibration means for use by the consumer in addition to providing for factory calibration.

In carrying out my invention in a preferred embodiment thereof, I provide a flatly disposed elongated subbase which is made at least partly of insulating material. Joined to the subbase at two points near opposite sides thereof is an elongated base composed of a concatenation of intertting conductive and insulating members which provides for the mounting near one end of an adjustable dial and cam structure for varying the setting of the thermostat. Near the other end of the base is the switch structure, while at an intermediate point va leaf spring is joined to the base for supporting a hat bimetal thermostatic element which operates the switch in response to temperature changes. A readily detachable cover is provided for the complete mechanism.

For a clear and more complete understanding of the invention, reference should be had to the accompanying drawingin which Fig. 1 is a front plan View of the thermostatic mechanism with the cover in section and portions cut away in order to reveal the operating parts; Fig. 2 is a side elevation view of the mechanism with the cover in section; Fig. 3 is a side sectional view of the thermostatic switch along the ilne 3-3 of Fig. 1; Fig. 4 is a top View of the mechanism with the cover in section; Fig. 5 is a sectional view along the line 5-5 of Fig. 1; while Fig. 6 is a sectional view along the line 6--6 of Fig. 1.

As shown in the drawing, all of the operating parts of the thermostatic switch which is designated generally by the numeral I0, are mounted in cooperating relation upon a llatly disposed elongated subbase II composed of two principal parts. One such principal part is a flatly disposed metal member I2 having a cut-out center portion I3 so that the metal member forms an outline around the device which resembles an irregular picture frame when viewed from the (Cl. 20o-139) rear. The thermostatic switch is preferably mounted vertically in the position shown in Figs. 1, 2, and 3. At the top, bottom and along both sides, the metal subbase member I2 is provided with right angle portions I4 projecting outwardly from the flat vertical portion. The second principal part of the subbase II is a flat rectangular member of insulating material I5 which is secured to metal member I2 by a plurality of horizontal projections I6 on right angle portions I4 along the sides of the subbase; member I5 does not extend the full length of member I2 as will be brought out in more detail subsequently but is positioned so that the upper and lower sides of the rectangle form two transversely disposed horizontal insulating portions intermediate the upper and lower extremities of member I2. Projections I6 are formed integrally with the angle portions I4 along the two sides of the metal subbase member and are bent to the position shown best in Fig. 4 to retain the insulating member I5 in place on metal member I2. Also cooperating in holding insulating member I5 in place are a pair of angle portions Il. Angle portions II are formed integrally with member I2 and lare connected thereto by sector portions I8. Portions I'I extend along the entire length of the inner side surfaces of insulating member I5 and in cooperation with projections I6 provide a very rigid connection between insulating member I5 and metal member I2 to form a unitary base member II. The ends of angle portions I'I abuttingshoulder portions on insulating member I5 at locations I9 prevent longitudinal movement of insulating member I5 with respect to member I2, while projections I4 in cooperation with projections I1 prevent lateral movement and projections I6 hold the insulating member I5 rmly against the flat portion of metal member i2.

The subbase II also includes an offset portion or boss I9 formed integrally with metal member I2 and having a longitudinally elongated screwreceiving opening 2D therein. Near the lower end of the subbase a second boss 2I is provided having a transversely disposed screw-receiving opening 22 therein. Bosses I9 and 2| with their respective openings 20 and 22 are used for securing the subbase II to a wall or other mounting surface, the horizontally disposed elongated opening in one projection and the vertically elongated opening in the other providing for the ready positioning and alignment of the subbase II. The remainder of the thermostatic mechanism and the cover, which are subsequently described in detail, are not in position at the time the subbase is installed.

The metal subbase member i2 is preferably formed from a single piece of metal by first punching out suitable openings and then forming the desired angular and offset portions by means of suitable dies. Insulating subbase member is preferably'cut from a thin iiat sheet of molded insulating material.

The thermostatic mechanism is secured to the subbase by two angular metal members 23 which serve also as terminal members. Each of the members 23 comprises a lower inwardly disposed iiat portion 24, an intermediate portion 25 joined at right angles at the outer edge of portion 24, and a second outwardly disposed fiat portion 26 joined to portion 25 at the outer edge thereof and positioned substantially parallel to portion 24. One of members 23 can be seen in Fig. 3 of the drawing, a portion of both of them can be seen in part in Fig. 1, but Figs. 4 and 5, perhaps, show these two members most clearly. Each portion 24 of a terminal member 23 has a pair of leg portions 21 projecting at right angles (upwardly in Fig. 5) beyond insulating member i5 on opposite sides of the upper horizontal portion of this member. Recesses are provided in the upper and lower edges of the upper horizontal portion of insulating member I5 to receive the leg portions 21 of terminal members 23 and these terminal members are secured to the base by assembling them on the insulating member |5 and then pinching together the oppositely disposed leg members on each terminal member 23. In addition the two individual legs of each leg portion 21 are spread apart to engage the sides of the recesses in member |5 to further aid in securing terminals 23 to member |5. One of the lower portions 24 of a terminal member 23 is tapped to receive a terminal screw 28, as shown in Figs. 1, 3 and 5, while the hole in the other portion 24, which is labeled 29 in Fig. 1, is not tapped since there is no electrical connection at this point. Screw 28 is provided with a washer 23a, while insulating member |5 is provided with an untapped hole beneath the terminal screw 28 to allow this screw to project through the insulating member as far as is necessary in order to make a mechanically tight electrical connection.

The terminal members 23 jointly support a base which supports the movable elements of the mechanism. This base includes a relatively small conductive member 30 secured to the lefthand (as seen in Fig. 1) terminal member 23 and a relatively large conductive member 3| connected to the righthand terminal member 23. Conductive member 3U, as best seen in Fig. 2, includes a irst fiat portion 32 which is secured to terminal member 23 in a suitable manner such as by a screw 33 engaging a recess in the lower edge thereof, an oblique intermediate portion 34 and a second fiat portion 35 offset from and substantially parallel to portion 32. Conductive member 3| includes a fiat portion 36 which is coplanar with portion 32 of the other conductive member but is separated electrically therefrom. Portion 36 covers a much larger area than portion 32, the latter extending only along the left side as shown in Fig. 1, while portion 36 as shown in Figs. 1 and 3 completely surrounds a circular cam member 31 which is described in detail subsequently. In addition to portion 36. member 3| includes a first oblique portion 36. a first fiat offset portion 33, a second of the length thereof together with a corresponding projecting portion 81a on the opposite surface to provide added strength and rigidity. Member 3| is secured to the righthand terminal member 23 in a suitable manner such as by a screw |25 engaging a recess in the lower edge of portion 36, thus connecting member 3| rigidly to the subbase through right hand terminal 23.

The coplanar conductive portions 32 and 36 jointly support a fiat insulating member 43, this member being secured to portion 32 by a pair of rivets 44. Member 43 is secured to portion 36 by a plurality of integrally formed projecting portions 45 on portion 36 extending through corresponding apertures in member 43, each such projection having a divided extremity portion which is spread apart to engage the sides of its corresponding aperture to firmly securel member 43 to member 36. Circular cam member 31, which is preferably of molded resinous insulating material. projects through an opening in portion 36 as previously mentioned, a shoulder portion 48 on cam member 31 engaging portion 36 and providing for the rotation of the cam member relative to portion 36. Insulating member 43 is provided with a larger opening than portion 36 through which the smaller inner end portion of the circular cam member 31 extends, as best seen in Figs. 3 and 5. An insulating spacing member 46 is positioned on the outer surface of portion 36 surrounding an intermediate diameter portion of the cam member 31 while a dial member 41 is positioned abutting the outer surface of spacing member 46, both outer members 46 and 41 being held in frictional engagement with the remainder of the cam assembly by a second shoulder portion 48 on cam member 31.

Cam member 31 has a central opening 49, the inner surface of which forms a helical cam serface 50. At the bottom of opening 49 a smaller opening is provided in which is positioned a member 5|, One end of member 5| is provided with a projecting flange portion 52 which engages a corresponding shoulder in the bottom of opening 49, while the other end of member 5| is provided with -a reduced diameter shank portion 5| just beyond the inner surface of cam member 31. The entire cam assembly is rotatably secured to portion 36 by a flatly disposedv resilient member 53 having an elongated opening 54 therein which is forced over the reduced diameter shank portion 5| of member 5| with the ends of member 53 in engagement with insulating member 43 thereby to hold the cam assembly in position. Member 53 can best be seen in Figs. 3 Iand 5. Rotatable circular dial member 41 has a knurled portion 55 around the circumference thereof to facilitate rotation of the dial by hand, while indicia 56 are provided on the outer surface of the dial to provide an indication of the setting of the thermostatic switch. The dial 41 is also provided with an arcuate slot 51 subtending an angle of more than degrees of the upper portion of the dial in this typical illustration. Through this slot projects a pointer 58 which cooperates with the indicia on the dial to indicate the setting of the switch. Pointer 58 has a base portion 59 extending along the under surface of the upper `portion of insulating member 43, and portion 59 is secured to member 43 by a pair of posts 60 which project' through member 43 and up through slot 51 in the dial to provide stops for the dial in cooperation with the end portions 6| of slot 51. In this manner the angle through which dial 41 may be rotated is limited to a predetermined magnitude, such as approxi-mately 180 degrecs.

Cam member 31 is rotatable with respect to dial 41 by overcoming the friction between these two members. To aid in rotating one with respect to the other, cam member 31 is provided with an arcuate ange portion 62 of increased diameter around the upper portion of the outer periphery of the'outermost surface, and portion 62 isprovided with a pair of indentations 63 to facilitate moving member 31 with the ilnger or by means of a suitable instrument while holding dial 41. The end shoulder portions 64 of flange 62 cooperate with a raised projection 65 on dial member 41 to limit the rotation of member 31 with respect to dial 41.

Provision is made for locking dial 41 comprising a small, flat, rectangular member 66 which is 'positioned beneath the dial and has a recess 61 near one end which embraces the righthand pin 68. The other end of member 61 is tapped to receive a screw 68 which projects from the front of the dial 41 through the slot 51, the head of the screw engaging the outer surface of the dial. In order to lock the dial it is necessary only to tighten screw 68, while loosening the screw unlocks it again.

Device I8 includes as the operating element a bimetal thermostatic member 69 which is supported centrally of the device by an electrically conductive resilient leaf spring 18 and operating arm 16. Spring 18 in turn is rmly secured to portion 39 of the subbase assembly by a pair of rivets 1| which extend through a plurality of insulating blocks 12, the rivets 1| and the blocks 12 being so constructed and arranged that spring 18 is electrically isolated from portion 39 of electrically conductive member 3|. Spring member 18 is preferably provided with outwardly projecting right angle portions 13 which fit in corresponding recesses in the center insulating block 12 to insure that member 18 will be held ilrmly without movement with respect to the base. Spring is connected electrically along the left side to portion 35 of conductive member 38, this preferably being accomplished by welding a pair of projections 14 on spring 18 to portion 35 along the joint 15.

The upwardly extending metal cantilever supporting arm 16 is secured to spring 18 in a suitable manner such as by a pair of rivets 11. At the upper end of member 16 bimetal element 69 is secured thereto in a suitable manner such as by a pair of screws |26 to form an electrical connection therebetween. The bimetal 16 is slotted where screws |26 pass through it to provide adjustment of the bimetal position. A calibrating screw 18 having a lock nut 19 is also provided near the end of member 16, the inner end of the calibrating screw 18 being biased into continuous engagement with the helical cam surface 58 of cam member 31 by the action of spring 18.

At the lower end of the device I8 there is provided a contact assembly which includes a movable contact 88 mounted on bimetal 69. Two eyelets |21 are used to secure an armature 8| to the end of the bimetal, armature 8| cooperating with a permanent magnet 82 which preferably has a high residual coercive force and is disposed in magnetic attractive relation with the armature 8| so as to provide a snap action in the engagement and disengagement of the circuit controlling contacts, these` contacts including movable contact 88 ited travel. Magnet 82 is supported by a nonmagnetic member 83 which is secured to portion 4| of the base in a suitable manner such as by a pair of rivets 84, member 83 having a pair of outwardly projecting portions 86 positioned on either side of reduced width angle portion 42 of the base and embracing magnet 82.

The relatively fixed contact 88 which cooperates with movable contact 88 in opening and closing a circuit is mounted on a cantilever spring member 89. Cantilever spring 89 and a second cantilever spring 98 are firmly secured in superimposed relation on the base structure by rivets 1| which connect them electrically to member 3|, while insulating blocks 12 isolate them from spring 18. Spring 89 is relatively weak and is biased toward bimetal 69 while spring 98 is relatively strong and is biased in the opposite direction. Spring 98 is provided with a projection 9| which embraces spring 89 and thereby restrains the latter in accordance with the position of spring 98. When the bimetal actuates contact 88 and contacts 88 and 88 close, spring 89 flexes and permits contact 88 to move inwardly a small amount until contact is made by spring 89, with spring 98, the distance of such movement depending upon the location of projection 9| with respect to the at portion of spring 98. When the bimetal 69 sets up a force tending to open the contacts by pulling the armature 8| away from the attractive zone of magnet 82 in order to open the contacts 88. 88, the described arrangement permits contact 88 to follow contact 88 until spring 89 engages projection 9|, after which the contacts part with a snap. This is to prevent chatter of the contacts. If such an arrangement is not used, chatter may result when the switch opens due to the fact that just before the armature pulls free of the magnet the force on the contacts must pass through zero which allows the circuit to break and remake.

The position of spring 98 and hence the relative positions of armature 8| and magnet 82 in the switch closed position are adjusted by a set screw 92. Set screw 92 has external threads engaging corresponding internal threads in an aperture in portion 4|, and for the purpose of preventing free movement is also threaded through a resilient projecting angle member 93 which may conveniently be formed integrally with member 83 and is thus secured to the base by rivets 84. An insulating member 94 is secured to set screw 92 by a lock nut 95 cooperating with the head 92a of the set screw. Member 94 is arranged for limited arcuate movement, this4 member having an opening 96 through which reduced width angular portion 42 of the base projects, the end portions 91 of member 94 adjacent opening 96 providing stops for member 94. As will be discussed in greater detail subsequently, member 94 and set screw 92 are used to adjust the diierential of the thermostatic switch. A projection 98 forming a pointer on member 94 is provided for cooperation with indicia 99 to indicate the differential adjustment. Indicia 99 are located on an offset portion |88 of metal subbase member |2 positioned along the outer edge of angular portion |4 along the bottom of member I2.

Provision is made in device |8 for the inclusion of one or two resistors, if desired. To provide a mounting for these resistors, the lower horizontal and a contact 88 having lim- 7 portion of insulating subbase member I5 is provided with two additional terminal members which may be identical to the righthand terminal member 23 (see Fig. l) on the upper horizontal portion of member I5. Each terminal member |0| includes a flatly disposed portion |02 positioned in engagement with member I5, each portion |02 having a pair of oppositely disposed leg portions |03 extending in recesses on opposite sides of member I and securing member |0I to member I5 in the same manner as described previously for leg portions 21 of terminal members 23. Each fiat portion |02 is provided with a tapped opening in which are positioned screws |04 having washers I04a. Screws |04' project through corresponding untapped openings in member I5 and provide for attaching connecting wires between washers |04a and portions |02. Each terminal member |0I also has an intermediate right angle portion |05 and an offset portion |06 substantially parallel to iiat portion |02. Screws |01 and washers |01a cooperating with portions |06 are provided for securing one terminal of each of the resistors, portions |06 being threaded to receive the screws while base I5 is provided with untapped openings |00 corresponding to the locations of screws |01 to provide space for the entry of the screws if necessary. If desired, portions |06 may be provided on their outer surface with depressions I06a to receive the I resistor terminal Wires.

A pair of resistors |09 and IIO, which may be respectively preheat and night set-back resistors, may be connected between terminals |0| and terminals 23, the upper terminal wire |09a of resistor |09 being secured between member 30 and lefthand terminal 23, and the upper terminal wire I Illa of resistor I0 being secured between member 3| and righthand terminal member 23, while the lower terminal wires I09b and ||0b of the resistors are secured respectively in recesses I06a. It will be understood that upper terminals 23 may also be provided with recesses, similar to recesses |06a in the lower terminals, to facilitate the installation of terminal wires I09a and IIOa.

It will be understood also that either or both of resistors |09 and |I0 may be omitted, if desired, and connections made directly to terminals 23 instead of to terminals |0I and thence through the resistors to terminals 23. In any event, terminals 23 can be utilized whenever needed whether terminals I0| are utilized or not, and in the normal connection for a night set-back resistor such as resistor IIO it will be necessary 5 to utilize the righthand terminal 23 for one of the external connections for the thermostat.

All of the screws in this device which are used either to fasten the base to the subbase or for external wiring are swaged on the end so that they cannot be readily removed and lost. v

The thermostatic switch I0 is provided with a cover which is designated generally by the numeral The cover I|I is specially formed and arranged so that it may be readily mounted and dismounted on the subbase to enclose the thermostatic switch mechanism, with both the manual temperature setting dial 41 and the manual differential adjustment member 94 projecting through the upper and lower ends respectively of the cover for operation externally thereof. A suitable enlarged opening |I2 is provided in the upper end of the cover III to permit the upper portion of dial 41 to extend therethrough. The

cover III also is provided with an enlarged portion I I3 which hooks over a projection I I4 on angular portion I4 along the upper edge of metal subbase member I2, portion I3 thus securing the upper edge of the cover. The lower end of the cover is detachably secured to the subbase by a pair of projections I I5 which engage a pair of resilient members IIB, the latter being secured to subbase member I2 in a suitable manner such as by rivets ||1 and extending outwardly from the subbase to form resilient catches as illustrated in Figs. 2 and 3. The side portions ||0 of the cover are preferably of molded resinous material while the center strip ||9 extending the full length of the cover and curving inwardly at both ends may be of brass. Brass strip ||9 may be conveniently secured to the plastic portion IIB of the cover by a pair of inwardly disposed angular portions |20 at the top and bottom, this construction permitting the brass strip to be assembled merely by snapping it into place on the plastic portion of the cover. A plurality of openings I2| are provided in the upper and lower end portions of strip IIS to provide for the circulation of air over the switch mechanism.

Before the strip IIS is assembled with the remainder of the cover a thermometer |22 is secured thereto in a central position, the thermometer being supported by a suitable support member |23 which is part of the molded case. A vertical slot |24 is provided in member IIS on the front of the device to enable the thermometer to be read, while suitable indicia are provided along the side oi the slot for use in determining the height of the uid in the thermometer.

The improved bimetal unit mounting structure of this invention enables the thermostatic bimetal operating element 69 to be formed of a bimetallic piece of material which is substantially straight at normal temperatures. Such a straight piece of bimetal maintains a higher degree of accuracy and sensitivity of control as it is never subjected to internal strains which become released in service or upon aging as do bimetal operating elements in a spiral, or U-shape. Moreover, the mounting of the normally straight bimetal element 00 in substantially parallel spaced-apart relation with the subbase II enables a free flow of room air through the various Ventilating openings in the tcp and bottom of the removable cover I|I directly over the surfaces of the bimetal element as indicated in Figs. 2 and 3. This enables the normally straight bimetal element 68 to respond readily yto slight changes in temperature of the ambient room air. The bimetal element 69 is positioned within the enclosing case at the maximum distance from subbase II, and the base in turn is spaced away from the wall by mounting bosses I3 and 2|; this serves to reduce the wall temperature effect upon the thermostat due to the intervening air spaces and thereby aids in making the bimetal element accurately responsive to room air temperature.

The cam assembly at the upper end of the device which provides means for adjusting the temperature setting of the thermostatic switch has two calibrating means. The first of these, which is intended primarily for factory calibration, is provided by set screw 10. By turning this screw the position of the upper end of bimetal B9 relative to the helical cam surface 50 formed, for example.'

can be adjusted, it being recalled that spring member 10 is biased so that the inner end of screw 18 always remains in contact with helical cam surface 50. In calibrating the thermostatic switch, if it is desired that bimetal 69 move contact80 to the closed contacts position at a lower temperature, set screw 18 is turned so that the upper end of bimetal 69 is moved closer to cam surface 50; this will cause bimetal 69 to operate at a lower temperature to close contacts 80, 88 at theV lower end of the bimetal, while turning set screw 18 so that 'the distance between bimetal 89 and helical cam surface 50 is increased has the opposite effect. Additional calibrating means for the cam mechanism are provided by the rotatable connection between cam member 31 and dial 41 which permits one to be rotated with respect to the other, it being understood that there Ais suicient friction between them that the two normally turn together when dial 41 is turned. The second calibrating arrangement is provided primarily for the benefit of householders who may feel that the factory calibration is not accurate due to varying conditions in individual heating and air conditioning installations and the like. If, for example, the householder feels uncomfortable at a particular temperature, such as 72, which he feels should be maintained, he can slip the cam member 31 onthe dial 41 so that the dial still reads 72 but the thermostat actually holds a temperature above r below this value, depending on the amount of relative rotation of member 31 with respect to dial 41.

The differential of the thermostatic switch,

that is, the difference between the temperature at which bimetal 69 closes the contacts 80, 88 and the temperature at which it opens them again is adjustable by moving member 94. This turns screw 92 in and out and decreases and increases the spacing of spring 90 with respect to the subbase. This in turn adjusts the spacing between armature 8| and magnet 82 in the closed contacts position, it being understood that armature never actually engages either magnet 82 or nonmagnetic supporting portions 85. The smaller this spacing is made, the greater the differential becomes because a greater force is required to pull the armature out of the attractive field of the magnet. Conversely, as the spacing between armature 8| and magnet 82 is increased the differential decreases. In a typical apparatus, the differential may be adjustable from 2 to 4 F., although the differential maybe readily made more or less by suitably proportioning the elements of the differential mechanism in order to conform to the requirements of a particular installation. Asmentioned previously, the indicia 99 in cooperation with pointer 98 indicate the differential setting of the device.

In operation, one side of an electrical circuit which is to be opened and closed by the thermostatic switch |0 is connected to the lefthand terminal |0| and thence through resistor |09 to lefthand terminal 23. A jumper may be substituted for resistor |09, if desired. From lefthand terminal 23 the electrical circuit is continued through conductive member 30 including portions 32, 34 and 35 in this order. Portion 35 is connected to spring 10 at junction 15 from which the electrical circuit continues through supporting arm 16 and then through screws |28 and bimetal 89 to movable contact 80. When contacts 80 and 88 are in engagement the circuit is completed through fixed Contact 88, spring 89,

l0 rivets 1|, portions 39, 38 and 36 of conductive member 3| and thence to righthand terminal 23. The other side of the external circuit is connected to righthand terminal 23. When the ambient temperature is below a predetermined value dependent upon the setting of the cam adjusting mechanism and the differential adjusting mechanism, bimetal 69 springs inwardly and causes -movable contact to engage fixed contact 88. This may, for example, energize an electrical control circuit which initiates the voperation of a heating apparatus to increase the room temperature. Then when the temperature increases to a second higher predetermined value dependent upon the setting of the differential mechanism, bimetal |59 swings outwardly, opening contacts 80 and 88 and cle-energizing the heater circuit.

Thus, it will be seen that I have provided a thermostatic device constructed of a relatively few parts which are simple and readily formed and which may be assembled to provide a rugged thermostat which is not susceptible to damage or to false operation due to shock or vibration. The thermostat is also easy to install, it being necessary only to provide two screws for fastening subbase to a wall or other supporting member by means of bosses I9 and 2| while the base. the operating mechanism and the cover are removed. If desired, a fiberboard or other shield, having holes for the electrical leads, may be placed between the subbase and the wall to prevent drafts due to the holes cut in the wall for the leads from affecting the bimetal element. Terminals 23 and |0| are already in place onthe subbase, and resistors |09 and ||0 may also be in place during this operation. Then after connections to the external control wires have been made to terminals 23 and |0| by means of screws 28 and |04 respectively, the base and operating mechanism assembly is pvt in place merely by loosening screws 33 and |25 sufficiently to insert the corresponding recesses in portions 32 and 3B respectively beneath the screw heads, after which the screws are tightened to hold the base with the operating mechanism mounted thereon rigidly in place. Thereafter, it is necessary only to put the cover in place by hooking projection portion I3 over projection |4 at the top of the subbase and springing proiections ||5 on the cover into place in engagement with members ||6 at the bottom of the subbase.

While I have illustrated and described my invention in a form useful primarily as a thermostatic switch for heating or cooling service, it will be understood that it may readily be adapted for use in controlling other conditions. For example, it may be converted from a thermostat as shown to a humidostat merely by replacing the bimetal element 69 of the thermostat with a special humidity responsive operating element. Such a humidity responsive operating element consists of a relatively thin metal strip which is united throughout its length to a strip of suitable humidity responsive material such as wood, cellulose or the like. It will be understood that this and other modifications may be made by those skilled in the art. Therefore, it should be understood that my invention is not limited to the preferred embodiment which I have illustrated and described but covers all modifications which fall Within the spirit and scope of the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A condition responsive switch comprising a flatly disposed elongated subbase at least a portion of which is made of electrical insulating material. a pair of conductive terminal members secured to said insulating portion on one surface of said subbase, an elongated base secured to said subbase by means of said terminal members and supported thereby, said base being positioned in spacedapart approximately co-extensive relation with said subbase,'said base comprising a first elongated conductive member connected to one ter-y minal member and a second shorter conductive member connected to the other terminal, said two conductive members jointly supporting near one end of said device a flatly disposed insulating member having a circular opening therein. a circular cam member having a helical cam surface rotatably positioned in said opening, a circular adjusting dial positioned in concentric interfitting jointly rotatable relation with said cam member, said cam member being selectively rotatable with respect to said dial to provide a first calibrating means, a conductive spring member sercured centrally of said base on said first conduccally to said spring, a conductive supporting arm l connected to said spring and extending longitudinally adjacent said helical cam surface, said spring biasing said arm toward said cam surface, a set screw extending through said arm and engaging said cam surface for adjusting the distance between said arm and cam surface to provide a second calibrating means, an elongated conductive condition responsive element having one end secured to said arm adjacent said cam member and extending in substantially parallel spaced-apart relation with said subbase and approximately coextensive with the intervening base, a movable contact positioned near the opposite end of said conditionresponsive element, and a cooperative fixed contact carried by said base and connected electrically to said first conductive member, said condition responsive element moving said movable contact into and out of engagement with said fixed contact in response to predetermined changes in said condition to make and break an electrical circuit between said terminal members through said contacts.

2. A thermostatic switch comprising a flatly disposed elongated subbase at least a portion of which is made of electrically insulating material, a pair of conductive terminal members secured to said insulating portion adjacent opposite sides of one surface of said subbase, an elongated base secured to and supported by said terminal members and positioned in spaced apart approximately coextensive relation with said subbase, said base comprising a first elongated conductive member connected to one terminal member and extending substantially the full length of said base and a second shorter conductive member connected to the other terminal, said two conductive members jointly supporting near one end of said switch a flatly disposed insulating member having a circular opening therein, a circular cam member having a helical cam surface rotatably positioned in said opening, a circular dial positioned in concentric interfitting jointly rotatable relation with said cam member, said cam member being selectively rotatable with respect to said dial, a conductive leaf spring member secured centrally of said first conductive member and insulated therefrom, means electrically connecting said second conductive member and said spring, a conductive supporting arm connected to said l2 spring and extending longitudinally adjacent said helical cam surface, said spring biasing said arm toward said cam surface, a set screw extending through said arm and engaging said cam surface for adjusting the distance therebetween to provide a calibration means for said switch, an elongated bimetal element having one end secured to said arm adjacent said cam member and extending in substantially parallel spaced apart relation with said subbase and approximately coextensive with the intervening base, an armature secured to the opposite end of said bimetal element, a permanent magnet secured to said base near the opposite end thereof, said permanent magnet cooperating with said armature to provide snap action of said bimetal toward and away from said base responsive respectively to a decrease in temperature below a predetermined value and an increase in temperature above a higher predetermined value, a movable contact carried by said bimetal, a relatively fixed contact carried by a relatively weak cantilever spring member supported centrally of said first conductive member and connected electrically thereto, said cantilever spring member being biased toward said bimetal, a second relatively strong cantilever spring mem, ber secured between said first cantilever spring member and said base in approximately parallel relation with said first cantilever spring, said second cantilever spring being biased away from said bimetal and having a projection thereon embracing said flrst cantilever spring and confining said first spring to a small movement between said embracing projection and said second spring,

- said bimetal forcing said first cantilever spring into engagement with said second cantilever spring when it moves toward said base into the contacts closed position, said first cantilever spring following said bimetal for a short distance until stopped by said projection thus causing said contacts to open when said bimetal moves away from said base, and adjustable stop means supported on said base for adjusting the position of said second cantilever spring to vary the gap between said armature and said permanent magnet when said contacts are engaged in order to vary the difference between said predetermined temperatures.

3. A thermostatic switch comprising a subbase .formed by a flatly disposed elongated metal subbase member having at least two mounting bosses projecting from one surface thereof and an insulating subbase member secured to the other surface of said metal subbase member, a pair of conductive terminal members secured to said insulating subbase member adjacent opposite sides thereof on the surface away from said metal subbase member. an elongated base as sembly secured to `and supported by said terminal members and positioned in spaced apart approximately coextensive relation with said subbase, said base comprising a first elongated conductive member connected to one terminal member and extending substantially the lfull length of said base, said first conductive member having 3 offset portions located progressively farther away from said subbase beginning at one end of said switch, the intermediate offset portion of said first conductive member being approximately centrally located, a. second shorter conductive member connected to the other terminal having a flatly disposed portion near said first end of said switch which is coplanar with the first offset portion of said first conductive member but isolated electrically therefrom. a

flatly disposed insulating member jointly supported by said coplanar portions of said conductive members on the under surface of said base between said conductive members and said subbase, said' first conductive member having a circular opening in said first oiset portion thereof and said flatly disposed insulating member having a circular opening coaxial therewith, a circular frictional spacing member positioned in coaxial relation with said openings on the outer surface of said first offset portion opposite said flatly disposed insulating member, a fiat circular dial having a circular opening therein coaxially positioned on the outer surface of said spacing member, a circular cam member provided with a helical cam surface rotatably secured in said four coaxial openings whereby` a temperature adjusting and Calibrating assembly is formed, said dial and said cam member being jointly rotatable with respect to said first offset portion through a portion of a complete rotation to provide for the temperature adjustment of said switch, and said dial and said cam member being selectively rotatable with respect to each other through a portion of a complete L rotation to provide a first Calibrating means, indicia on said dial, a pointer secured to said flatly disposed insulating member and cooperating with said indicia to indicate the setting of said switch, a conductive spring member secured to said intermediate offset portion of said first conductive member and insulated therefrom, means electrically connecting said second conductive member to said spring, a conductive supporting arm connected to said spring and extending longitudinally adjacent said helical cam surface, said spring biasing said arm toward said cam surface, a screw extending through said arm and engaging said cam surface for adjusting the distance between said arm and said cam surface whereby a second calibrating means is provided for said switch, an elongated bimetal element having one end secured to said arm adjacent said cam member and extending in substantially parallel spaced apart relation with said subbase and approximately coextensive with the intervening base, a movable contact carried by said bimetal near the opposite end thereof, a relatively fixed contact carried by a first relatively Weak cantilever spring member supported on said intermediate offset portion of said first conductive member and connected electrically thereto, said first cantilever spring member being approximately parallel to the third offset portion of 'said first' conductive member and biased toward said bimetal, a second relatively strong cantilever spring member supported in superimposed relatlon on said intermediate oiiset portion between said first cantilever spring member and said base in substantlally parallel relation with both, said second cantilever spring being biased away from said blmetal and having a projection 'thereon embracing said first cantilever spring and confining said iirst spring to a small movement between said projection and said second cantllever spring, said bimetal forcing said nrst cantilever spring into engagement with said second cantilever spring when it moves toward said base into the contacts closed position, said first cantilever spring following said bimetal for a short distance when said bimetal moves away` from said base until stopped by said projection on said second cantilever spring which causes said contacts to open, adjustable stop means supported on said third offset portion of said base for adjusting the position of said second cantilever spring toward and away from said third ofl'set portion to vary the travel of said bimetal toward said base in the contacts closed position, an armature secured to the end of said punetal element adjacent said movable contact, a permanent magnet secured to said third oset portion of said first conductive member in spaced apart relation with said armature, said permanent magnet cooperating with said armature to provide snap action of said bimetal toward and away from said base in closing and opening said contacts in response respectively to a decrease in temperature below a predetermined value and an increase in temperature above a higher predetermined value, the position of said adjustable stop means relative to said third offset portion determining the difference between said predetermined temperatures.

RALPH M. MANNING.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,171,273 Cunningham Aug. 29, 1939 2,250,135 Lindemann July 22, 1941 2,276,852 Lynch Mar. 17, 1942 2,505,938 Biermann et al. May 2, 1950 

